This invention relates generally to supervisory systems and, more particularly, to an improved remote supervisory system that utilizes existing telephone company circuits and equipment for monitoring and reporting the existence of alarm conditions at a telephone subscriber premises and for enabling subscribers to exercise control functions at, and to transmit messages to, their premises from remote locations.
In many cases, it is desirable to provide continuous supervision of certain premises, such as homes, leisure homes, offices and the like, during the absence of those who normally occupy them. If any abnormal conditions exist at the premises, it is desirable that these conditions be reported to some entity which can take corrective action. It has been recognized that one possible solution to this problem is to use the existing telephone circuits over which the subscriber receives telephone service as the means for transmitting alarm reporting signals. At least two basic methods have heretofore been contemplated or used to provide this kind of supervision over the telephone networks.
In a first method, any abnormal condition at the subscriber location causes specially designed auxiliary equipment there to create an off-hook condition on the subscriber's circuit. Upon sensing and recognizing that a dial tone has been received on the circuit, the auxiliary equipment automatically dials a number which has been designated to receive the alarm reports. The equipment must then make sure that the connection to the called number has been completed. Thereafter, it must transmit the identification of the subscriber and the nature of the emergency. If the number which has been designated to receive the alarm report is busy, the whole sequence has to be repeated until this number has been reached.
The disadvantages of the first method lie in the additional complexity of having the auxiliary equipment detect and recognize dial tone, busy signals and call completion, and of having it store and transmit the number designated to receive the alarm reports and the customers identification number. Also, if the number designated to receive the alarm report is busy, the method fails to meet the general requirement that alarm conditions be forwarded to a location which is remote from the supervised premises at the earliest possible moment. Some emergencies, such as fire, can cause the destruction of the auxiliary equipment at the subscriber's premises and/or destruction of the subscriber's telephone line before the report is ever made.
In a second method, the telephone company central office equipment is modified so that it periodically transmits an interrogation signal over the telephone circuits of those subscribers that have requested the remote supervisory service. Reception of the interrogation signal at the subscriber location activates specially designed auxiliary equipment there which interrogates various alarm condition sensors at the premises, and which transmits signals over the subscriber's circuit that are indicative of the conditions at the premises. The interrogation signals are used to initiate a temporary off-hook condition and to activate the condition sensing and reporting auxiliary equipment at the subscriber's premises. The interrogation signals used in systems of this type must be different from the signals which are normally generated in the course of completing any call to the subscriber's location by the central office equipment. The interrogation signals may, for example, be in the form of an abnormally high DC voltage or a specially coded AC signal which is applied to the subscriber's circuit by the central office equipment. Because of the need for these special interrogation signals, special apparatus, such as bridging relay contacts or the like, is required at the central office to obtain access to the subscriber's circuit. The need for such special circuit accessing apparatus represents an objectionable complication at the central office.
It would be highly desirable if a telephone circuit supervisory system were available which did not have the complexity or other disadvantages of the above-discussed prior systems.
There are also many occasions when absent subscribers would like to exercise control functions at their premises from a remote location. Such functions might include energizing a group of lights to illuminate a driveway or entrance hall in a residence, activating an air conditioning system, changing a thermostat setting on a heating system, or the like. An absent subscriber may also want to leave messages for other occupants who are at the premises or who are expected to return to the premises before him. In their simplest form, the messages may cause the operation of a relay at the subscriber's premises that illuminates certain written instructions such as "take food out of the freezer" or "call XYZ". In a slightly more complex form, the message may cause the illumination of a single or multidigit number which refers to prearranged instructions. In still other occasions, the absent subscriber may want to transmit longer messages and have them recorded at his premises. It would also be highly desirable if these control and message functions could be provided along with the remote supervisory functions previously discussed as part of a single improved system.